In recent years, in addition to CRT (Cathode Ray Tube) display apparatuses, various display apparatuses, such as liquid crystal display apparatuses, plasma display apparatuses and organic EL display apparatuses, have been developed and commercialized.
Display apparatuses, such as the plasma display apparatuses, which carry out impulse display (display carried out only during a light emitting period) normally use time-division driving to carry out gradation display. Moreover, some of display apparatuses, such as the liquid crystal display apparatus and the organic EL display apparatus, which carry out hold display (display of keeping holding an image of a previous frame until a new image is written) use the time-division driving to, for example, prevent unfocused moving images. Note that the time-division driving is a driving method for dividing one vertical period (one frame) a plurality of sub-frames, and writing a signal to each pixel more than once.
For example, the time-division driving in the liquid crystal display apparatus is disclosed in Patent Documents 1 and 2.
Moreover, image signals of various formats which are different in pixel size and/or frequency depending on image sources (television waves, personal computers, videos, games, etc.) which supply image signals are input to recent display apparatuses. However, in a display panel, formats such as a resolution (pixel size) and a refresh frequency (frequency) are fixed. Therefore, when the image signal which is different in format from the display apparatus is input to the display apparatus, image processing is carried out to convert the format of the input image signal into the format of the display apparatus.
That is, as shown in FIG. 7, when a digital image signal whose format is different from the format that can be displayed in a display panel 100 is input to the display apparatus, the display apparatus causes an image processing circuit 101 to carry out format conversion so that the digital image signal can be displayed in the display panel 100. Moreover, when the input image signal is an analog signal, the display apparatus causes an A/D converter 102 to convert the analog signal into a digital signal, and then carries out the format conversion. Moreover, in addition to the format conversion, the image processing circuit 101 may carry out image processing, such as edge enhancement and tone correction.
Moreover, when carrying out the image processing, the display apparatus which carries out the time-division driving divides the input image signal of one frame into image signals corresponding to a plurality of sub-frames. For example, when one frame is 800H (A blanking period is included. Moreover, H denotes one horizontal period.), and is divided into two sub-frame with a split ratio of 1:1, the period of each sub-frame is 400H. Moreover, luminance of each sub-frame is determined so that average luminance of the sub-frames is equal to the luminance of the input image signal.    Patent Document 1: Japanese Unexamined Patent Publication No. 296841/2001 (Tokukai 2001-296841, published on Oct. 26, 2001)    Patent Document 2: Japanese Unexamined Patent Publication No. 22061/2003 (Tokukai 2003-22061, published on Jan. 24, 2003)    Non-Patent Document 1: Hironari TANAKA, Yuki SATO, Hiroaki KATODA, “42 PDP, EMC technique of ‘Plasmavision (trademark)’”, FUJITSU GENERAL TECHNICAL JOURNAL 1999 No. 1